【工具类】排序工具类

List、Map 按日期倒序排序

import com.alibaba.fastjson.JSONObject;

import java.text.SimpleDateFormat;
import java.util.*;

public class SortUtil {


    /**
     * list按日期排序 倒序
     *
     * @param list
     * @param dateKey 排序的字段名
     * @param dateFormat 排序的日期格式
     */
    public static void ListSort(List<JSONObject> list, String dateKey, String dateFormat) {
        Collections.sort(list, new Comparator<JSONObject>() {
            @Override
            public int compare(JSONObject n1, JSONObject n2) {
                SimpleDateFormat format = new SimpleDateFormat(dateFormat);
                try {
                    Date dt1 = format.parse(n1.getString(dateKey));
                    Date dt2 = format.parse(n2.getString(dateKey));
                    if (dt1.getTime() > dt2.getTime()) {
                        return -1;
                    } else if (dt1.getTime() < dt2.getTime()) {
                        return 1;
                    } else {
                        return 0;
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return 0;
            }
        });
    }


    /**
     * map按日期key排序 倒序
     *
     * @param map
     * @param dateFormat 排序的日期格式
     */
    public static <E> Map<String, E> MapSort(Map<String, E> map, String dateFormat) {
        Map<String, E> sortMap = new TreeMap<>(
                new MapKeyComparator(dateFormat));
        sortMap.putAll(map);
        return sortMap;
    }

    static class MapKeyComparator implements Comparator<String>{
        private String dateFormat;
        public MapKeyComparator(String dateFormat) {
            this.dateFormat = dateFormat;
        }

        @Override
        public int compare(String s1, String s2) {
            SimpleDateFormat format = new SimpleDateFormat(dateFormat);
            try {
                Date dt1 = format.parse(s1);
                Date dt2 = format.parse(s2);
                if (dt1.getTime() > dt2.getTime()) {
                    return -1;
                } else if (dt1.getTime() < dt2.getTime()) {
                    return 1;
                } else {
                    return 0;
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            return 0;
        }
    }

}

使用：

public void listSort() {
    List<JSONObject> dateGroupList = new ArrayList<>();
    SortUtil.ListSort(dateGroupList, "date", "yyyy-MM-dd");
}

public void mapSort() {
    List<JSONObject> countList = mapper.selectList();
    // 按月分组
    Map<String, List<JSONObject>> collect = countList.stream()
            .collect(Collectors.groupingBy(item -> item.getString("date").substring(0, 7)));
    collect = SortUtil.MapSort(collect, "yyyy-MM");
}

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